1. Field of the Invention
The present invention relates to a small boat or watercraft, and more particularly to a small boat or watercraft having sponsons attached to left and right side walls that form a boat body.
2. Description of the Background Art
A small boat for gliding over the surface of a sea or a lake is known in the background art. A small propelled boat driven by taking in water from the bottom of the boat and spraying the water to the rear as a result of attaching a jet propulsion unit to the rear of the boat body and driving this jet propulsion unit with an engine is one of these types of small boats. This small boat may have sponsons extending longitudinally and being provided on left and right side surfaces of the boat body.
For example, Japanese Patent Laid Open No. Hei. 10-76990 (FIG. 2), the entirety of which is hereby incorporated by reference, depicts a small boat having sponsons as described hereinabove. This type of small boat is described in greater detail hereinafter with respect to the accompanying drawings. FIG. 9 is shows the basic structure of a small boat of the background art. The small boat 100 has a jet propulsion unit 103 provided on the stem 102 of the boat hull 101, and left and right sponsons 106 and 107 are respectively provided on rear sections of left and right side walls 104, 105. By attaching the sponsons 106, 107 on the left and right side walls, the left and right sponsons 106, 107 respectively jut outwards from the side walls 104 and 105.
A water jet is sprayed backwards from a steering nozzle 117 of the small boat 100 and the small boat 100 is moved in a straight line. When the small boat 100 is moving in a straight line, upper parts 108 and 109 of the left and right sponsons 106, 107 lift up from the water surface 111, and respective gliding sections 112 and 113 of the left and right sponsons 106 and 107 come into contact with the water surface 111. In this way, a large surface area of the hull is in contact with the water when the small boat 100 is moving.
FIG. 10(a) and FIG. 10(b) show an example of a turning operation of the small boat of the background art. In FIG. 10(a), during straight line movement of the small boat 100, a rider 115 operates a steering handle 116 as shown by arrows a1 to cause the steering nozzle 117 at the stern 102 to swing as shown by the arrow b1.
In FIG. 10(b), by moving the steering nozzle 117 to swing the water jet 118, water from the steering nozzle 117 is sprayed in an inclined direction, as shown by arrow c1. Accordingly, the stern 102 of the hull 101 is made to move in a rightward direction as shown by the arrow d1, and the small boat 100 begins to turn left. The small boat 100 then tilts to the left side, and the left sponson 106 sinks into the water. Therefore, the water resistance in the sideways direction with respect to the left sponson 106 becomes larger, and a movement amount of the stern 102 in the right direction is kept relatively small.
FIG. 11 shows an example of the small boat of the background art during a turning operation. An amount of movement of the stern 102 in the direction of arrow d1 is kept relatively small, and the small boat turns through a large arc as shown by the turning locus 119.
However, the small boat 100 has had many applications in recent years. For this reason, if parts suitable for turning through a large arc turning locus (large turn) or parts suitable for turning through a small arc turning locus (small turn) are provided in the small boat 100, the user selects a desired small boat 100 according to the application. Therefore, in order to allow a small boat to be used with a number of different applications, it is desired to make practical use of a small boat that turns through a small arc turning locus compared to the small boat of the background art.